The modern internal combustion engine usually incorporates a pulley drive system for powering accessories driven by the engine crankshaft. The accessories typically include an air conditioning compressor, a power steering pump, a water pump, and an alternator. Such accessories make up the front end accessory drive system (or “FEAD system”). Each of the accessories requires a driven pulley.
A front end accessory drive belt is trained around pulleys to supply power from the crankshaft of the engine to the accessories. The drive belt makes frictional contact with the face of the pulleys. Drive belts developed from the flat leather belt to V-belts and more recently to multi-V or serpentine belts. Most drive belts used today are formed from a flexible reinforced polymeric material.
However, to reduce both production cost and packaging, automobile manufacturers have more recently adopted low modulus or stretch fit belts that, unlike the widely-used multi-V or serpentine belts, have an effective degree of elasticity because of reinforcing cords made from polyamide material. The reinforcing cords of the most prevalent serpentine belt used today incorporate relatively inelastic aramid or polyester cords. The modern stretch fit belt is thus finding increased usage on FEAD systems to transmit torque from the engine crankshaft to one or more engine mounted accessories as is the case with traditional belts.
Stretch fit belt systems have a cost and package advantage over standard FEAD system belts that require and automatic spring loaded belt tensioner. No tensioning is required for stretch fit belts as these belts are self-tensioning. While having the appearance of conventional serpentine belts, stretch fit belts generally cannot be used on vehicles designed for use with standard drive belts. However, in some cases, it is possible to use a stretch fit belt on vehicles designed for use with conventional serpentine belts. This requires removal of the automatic tensioner and potentially some re-routing of the belt path.
The disadvantage of stretch fit belts is in the area of installation and service. The length of the stretch fit belt is actually less than the actual working length. However, when installed, the stretch fit belt is automatically tensioned. Installation is difficult because of assembly plant cycle time and the fact that the stretch fit belt has to be stretched over the pulley flanges for installation. This requires specialized tools that take up manufacturing line space and can also slow down cycle time. Belts are often cut off in service, creating additional cost for the customer, as a new belt is required even if the stretch fit belt is not the reason for the vehicle service.
As in so many areas of vehicle technology there is always room for improvements related to the design of a system for use with the modern stretch fit belt. Particularly, it would be advantageous to provide a modified FEAD system that can be readily adapted for use with a stretch fit belt without the need for specialized tools.